1. Field of the Invention
The present invention relates generally to a mobile communication system, and more particularly, to a method and apparatus for managing active sets of a terminal.
2. Description of the Related Art
Recently, in wireless communication systems, a distributed network structure and/or a flat network structure have been proposed, extensions of which are easier. Generally, the distributed network structure is composed of a base station(s) and a gateway. The distributed network structure has a simpler structure than the conventional wireless communication system, which is composed of a base station, a data controller and a gateway.
FIG. 1 is a diagram illustrating an example of a general distributed network structure.
Referring to FIG. 1, the general distributed network structure includes a gateway 101 for connecting a radio access network to an external network, base stations 102, 103 of the radio access network, and a wireless terminal 104.
The distributed network structure is characterized in that many control functions located in the conventional data controller are included in the base stations or the gateway. In addition, the distributed network structure, unlike the conventional network structure, allows more independence between base station nodes. That is, the distributed network structure allows the base stations to independently manage their own resources, and also allows the base stations having different protocol versions or communication setups to coexist in one system. In an example of FIG. 1, base station 102 and base station 103 can be different in the protocol version used for wireless access. In addition, the two base stations can allocate resources to one terminal independently of each other, or can exchange control messages with the terminal independently.
Further, the distributed network structure allows most terminal-related information to be stored and managed independently in each base station. Moreover, the distributed network structure assumes that the base stations can independently allocate and withdraw resources to/from a terminal. For example, when there are two base stations, base station A and base station B, base station A can independently allocate wireless resources to a particular terminal regardless of which wireless resources base station B has allocated to the particular terminal. In the distributed network structure, a terminal should transmit reception strength information of a pilot channel to base stations A and B independently in order to support independent resource management of each base station.
When different base stations allocate resources independently in this way, there is a possible problem that a sum of the number of resources allocated by each base station exceeds the number of resources manageable by the terminal. For example, in the case where the number of active sets supportable by a terminal is 3 (i.e., the terminal can receive wireless resources allocated in a total of 3 sectors), if base stations A and B each allocate wireless resources for two sectors therein to the terminal, the number of resources allocated to the terminal, i.e., the number of active sets, is 2 in each base station, which is less than the maximum number of active sets supportable by the terminal. However, when the numbers of resources allocated in all base stations are summed, if the number of active sets is 4, it may exceed the maximum number of active sets supportable by the terminal. That is, as different base stations independently allocate resources, the number of active sets manageable by one terminal may exceed the maximum number of active sets supportable by the terminal, so that the active sets manageable by the terminal may be allocated abnormally.
Therefore, there is a demand for a method and apparatus in which a terminal of a mobile communication system can efficiently manage active sets.